whether what appears to our senses and imaginations be true or not.

the stoics say that what the senses represent is true; what the imagination, is partly false, partly true. epicurus that every impression of the sense or imagination is true, but of those things that fall under the head of opinion, some are true, some false: sense gives us a false presentation of those things only which are the objects of our understanding; but the imagination gives us a double error, both of things sensible and things intellectual. empedocles and heraclides, that the senses act by a just accommodation of the pores in every case; everything that is perceived by the sense being congruously adapted to its proper organ.